Al Simmons was a government assassin until he was killed and sent to Hell where he was given a choice, to remain in eternal purgatory or return to the mortal plane as a Hellspawn. But it's a deal that Spawn intends for the Devil to regret...
This movie was the last acting role of Nicol Williamson (Cogliostro) who chose to retire afterwards.
Clown refrences this movie when he says that Spawn can be Jimmy Stewert and he will be Clarence. He also paraphrases a famous quote from this film when he says "Everytime someone farts a demon gets its wings."